2005 Grand am 6cyl heavily leaking coolant

Do you see coolant on the ground? If not .... it's going somewhere . Make sure you check your oil for foaming ... and pray to God you don't have a quad 4 engine because that job is a real bear

Have you checked the usual places like upper and lower hoses, water pump, heater hose to and from the firewall? If it's straight coolant under the car I don't expect a blown head gasket. If it's coolant mixed with oil and junk.... maybe...

Opps ... gotta read the posts more thoroughly .. If it's on the ground and a 6 cylinder it sounds like a hose (perhaps a heater hose) That mechanic is remembering a big problem Pontiac had with the coolant attacking the head gasket in that time frame

Just look around and find the source of the water. With that much coming out, it should not be difficult to determine what failed so it can be replaced. Water leaks are about the easiest to resolve. Very doubtful it is a head gasket buit that would be the most difficult and expensive to repair. All other components are Radiator, hoses & clamps, Water pump, and thermistat & housing. Fill it up and look for the source!